Technical Field
Exemplary embodiments of the present invention relate to an acoustic device employing a Helmholtz resonator, and further relates to an electronic device and an image forming apparatus employing the acoustic device.
Background Art
Various sounds are generated when various driving devices are driven or a polygon mirror is rotating in the image forming apparatus employing the electrophotographic method. Conventionally, an image forming apparatus including an acoustic device employing a Helmholtz resonator as a structure capable of absorbing sounds generated during image formation, is known.
The Helmholtz resonator is formed of a cavity with a certain volume and a port or a neck. If a static volume of the cavity is V, a cross-sectional area of the port is S, a length of the port in the connection direction is H, and acoustic velocity is c, then a resonant frequency f absorbed by the Helmholtz resonator is obtained by the following formula (1).f=c/2×{S/(V×H)}1/2  (1)
In an acoustic device employing the Helmholtz resonator, the cavity needs to be sealed from the external portion to obtain the desired absorption effect.
Based on the above equation (1), it is clear that the volume V of the cavity should be increased as a method of absorbing low-frequency sounds of less than 1,500 [Hz].